1. Field of the Invention
The present invention relates to a recording/reproducing apparatus for recording servo information on a disk medium, and then reading the servo information and performing servo control of a head.
Recently, due to the increased amount of information being processed in computer systems, the amount of information to be stored in a magnetic disk apparatus has increased. Therefore, miniaturization and increased storage capacities of storage media of information storage apparatuses are required. Further, high-density storage media and high-performance recording/reproducing apparatuses are demanded.
2. Description of the Related Art
FIG. 1 shows a plan view of one example of a magnetic disk apparatus in the related art. In the magnetic disk apparatus 11, an actuator 12 includes a predetermined number of arms 13 each of which has a magnetic head 14 at a projecting end thereof via a supporting-spring mechanism 13a. A base of each arm 13 is pivotably supported by a pivot 15.
A rotational supporting unit 16 is provided at the other end of the arm 13. A coil 17 is wound on the rotational supporting unit 16. Magnets 18a and 18b are fixed below the coil 17. A VCM (Voice Coil Motor) is formed by the coil 17 and magnets 18a and 18b.
A predetermined number of magnetic disks 20 are fixed onto a spindle 19 of a sensor-less spindle motor (not shown in the figure) and are rotated. In the actuator 12, an electric current flows through the coil 17 via a circuit substrate 21 and a flexible print board 22, and thus the arms 13 are rotated so that each of the heads 14 moves along a radial direction of each of the disks 20.
In this magnetic disk apparatus 11, a seeking control is performed for positioning the magnetic heads 14 at predetermined tracks in the magnetic disks 20. This seeking control is performed in a closed-loop servo control method in which servo information previously recorded on the magnetic disks 20 is read for the seeking control.
A servo-area servo method and a data-area servo method are included in the servo control method. In the servo-area servo method, a magnetic disk which has the servo information recorded in a special servo area in the disk is used. In the data-area servo method, a magnetic disk which has the servo information recorded in a data area in the disk is used.
The servo information is recorded in each track or each sector in the magnetic disks 20 at predetermined positions common to the magnetic disks 20. In order to read predetermined servo information from the magnetic disks 20, an index recorded in each track of each of the magnetic disks 20 is previously detected, index detection thus being performed. A recording position of the servo information and then positions of the magnetic heads 14 are detected based on the detected index.
FIG. 2 illustrates an index pattern in a magnetic disk in the related art. FIG. 2 shows a case of a sector servo method in which sector servo information 24 is recorded in each sector of a predetermined track in the magnetic disk 20. The sector servo information 24 is recorded, for example, in an AGC (Automatic Gain Control information) region 24.sub.1, in an SM (Servo Mark information) region 24.sub.2, an ID and INDEX (writing and reading index information) region 23.sub.3, and a POSITION (position information) region 24.sub.4 shown in FIG. 2.
Sector servo numbers (for example, 0 through 60) and an index pattern are recorded in the ID and INDEX region 24.sub.3. The index pattern is formed by a pattern in which "0" is allocated for a position at which the sector number is "0" and "1" is allocated for the other positions. The "0" in the index pattern acts as an index, and an index pulse is generated when "0" is detected. Thus, the above-mentioned index detection is performed.
Servo information is recorded in each of the magnetic disks 20 in a manner in which positions at which the servo information are recorded overlap one another between recorded tracks of the disks 20.
FIG. 3 shows a spatial relationship of the positions between disks 20 in the related art at which the servo information is recorded. FIG. 3 shows an example disclosed in Japanese Laid-Open Patent Application No. 2-304784. In this example, the servo information is recorded in the tracks TRK0 through TRK3 of the disks 20 in a manner in which the positions at which the servo information is recorded overlap one another between the tracks TRK0 through TRK3 of the disks 20 in a time series manner. When servo information is recorded or written in sectors (0, 0), (0, 1), (0, 2), and (0, 3) of the tracks TRK0 through TRK3 shown in the figure, a head 14.sub.0 selected from the magnetic heads 14 writes the servo information to the sector (0, 0) of the track TRK0. Then, after the completion thereof, a head 14.sub.1 selected from the magnetic heads 14 writes the servo information to the sector (0, 1) of the track TRK1. Thus, after completion of servo-information writing to one sector, servo-information writing to a subsequent sector is performed. In this manner, the servo information is written to the four sectors (0, 0) through (0, 3).
In the related art, as shown in FIG. 2, one index pattern is provided for the relevant servo information, and the index detection is performed by detecting only the one index pattern. Therefore, if the one index pattern is missing for some reason, an index error occurs and any normal operation cannot be performed until a subsequent index pattern is appropriately detected. Thus, performance of the magnetic disk apparatus is degraded.
Further, redundancy is not sufficiently high if only one index pattern is provided for the relevant servo information. Therefore, an index detection margin is not sufficiently high and thus performance degradation may also occur by this cause.
Further, in the related art, as shown in FIG. 3, the positions of the relevant servo information overlap one another between the tracks of the disks. Therefore, after the completion of servo-information writing on a sector of a track of a magnetic disk, it is necessary to wait for approximately one rotation of the disks 20 before starting servo-information writing to a sector of a track of a subsequent disk. As a result, the time required for writing the desired whole servo information and for verifying it for the entirety of the disks 20 is a considerably long time. In fact, this time results from multiplying the time required for writing the servo information for one track by the number of servo frames for each track and then multiplying this result by the number of cylinders of the disks 20. Thus, the servo-information writing or recording work is troublesome.